Which remote desktop app is best ?

There are various remote desktop services such as logmeinrescue, gosupportnow, GoToMyPC etc. However, I would prefer an appliance based deployment model such as Bomgar or RHUB appliances, as it is easy to use and there are no hassles of monthly payments. It is only a onetime cost.

If you're on a Mac, I'd personally recommend the built in screen sharing application. You can access it by accessing "Connect to Server" in the Go menu in the Finder menu bar. Then in the server address field, enter vnc://your-server-ip.